1. Technical Field of the Invention
The present invention relates to a hot stand-by switching apparatus which comprises a signal output means for outputting an active signal, or a preparative signal, and switches connected with the input terminals of an active transmitter and a preparative transmitter, respectively.
2. Description of the Prior Art
Conventionally, switching means for replacing an active power amplifier by an preparative power amplifier are connected with the output terminals of these amplifiers, as disclosed, for example, in JP 9-331275 A (1997).
Further, one of the conventional hot stand-by switching apparatus as disclosed in JP 3-270515 A (1991) comprises a directional coupler, wherein local oscillators, power sources for the local oscillators, and variable attenuators for transmitters are controlled.
However, the switching devices for RF power are expensive. Further, the conventional hot-stand-by switching apparatuses as mentioned above are poor in reliability, because only one switching device is employed commonly for both of the active and preparative circuits.
Furthermore, the time required for switching becomes long and the switching control becomes complicated, because sequential controls for stabilization are required, when stability at the times of rise-up and fall-down in frequency and output level of the above-mentioned oscillators and variable attenuators is not sufficiently high.
Therefore, an object of the present invention is to provide a hot stand-by switching apparatus which utilizes cheaper switching devices for high power RF signal.
Further, another object of the present invention is to provide a hot stand-by switching apparatus which stabilizes the frequency and the output level at the rise and fall times.
The hot stand-by switching apparatus of the present invention comprises a first transmitting means and a second transmitting means, wherein the first transmitting means comprises a first modulator, a first switch for turning on and off the output from the first modulator, and a first transmitter for amplifying the output from the first modulator through the first switch, and, likewise, the second transmitting means comprises a second modulator, a second switch for turning on and off the output from the second modulator, and a second transmitter for amplifying the output from the second modulator through the second switch. Furthermore, the hot stand-by switching apparatus of the present invention comprises a distributor for distributing an input signal to the first and second modulator, and a controller which selects the other transmitter, when one of the above two transmitters does not work well.
In short, the hot stand-by switching apparatus of the present invention comprises a signal output means for outputting an active signal, or a preparative signal, and switches connected with the input terminals of an active transmitter and a preparative transmitter, respectively.
According to the present invention, the hot stand-by switching apparatus is cheap and reliable, because a passive device such as a coupler or a directional coupler is employed as a switching means for turning off the active side and turning on the preparative side. Further, the switching device is cheaper and more reliable than the RF power switch, because the switching is executed in an intermediate frequency range.
Further, according to the present invention, the rise time and fall time for switching become shorter than in the conventional case wherein the oscillator or variable attenuator is controlled. Furthermore, any sequential control is not required at all, because the stability in frequency or output level is not irrelevant at all.